1997 legacy gt will idle high and take off like a rocket and at times idle low and be very sluggish taking off. Any suggestions?

. Ensure there's no air in the cooling system.

. Clean the throttle plate and throttle body with Carburetor and Throttle Body Cleaner.

. Clean/replace the Idle Air Control Valve.

If the problem persists, you may need to replace the Ignition Control Module.